This is a nationalization of PCT/FR00/01155, filed Apr. 28, 2000, and published in French.
1. Field of the Invention
The present invention relates to the connection and laying of the successive parts of an offshore supply line from a vessel performing installation operations, particularly in very great depths of water.
It applies to any supply line intended to carry a fluid, an electrical current, optical signals or information, and in particular to rigid or flexible tubular supply lines, umbilicals and electrical cables, whose behaviour in the vertical plane of the stretch of water is completely similar whatever the transverse rigidity of the supply line, provided that the depth of the said stretch of water exceeds 500 to 600 meters; the curvature adopted by the supply line under such conditions, whatever its nature, being substantially equivalent to the mathematical curve known as a catenary curve, since the effects of the rigidity of the supply line on the resulting curvature are secondary relative to the effects of gravity under these operating conditions.
The word xe2x80x9cvesselxe2x80x9d means any movable floating unit adapted to allow the laying of a supply line.
2. Description of the Related Art
The connection of the supply line parts requires the already submerged supply line part to be held, the new supply line part to be presented to the end of this part, the assembly tools to be operated and the supply line to be guided for laying in the sea.
Laying apparatuses are known which comprise, on board a vessel, (A) a variable inclination support equipped with means for supporting the weight of the already submerged supply line part and keeping available within an assembly plane the above-water end of this supply line part, means for receiving a new supply line part in accordance with the longitudinal axis of laying of the supply line and bringing it into the said assembly plane, and guide means, (B) means constituting a horizontal pivot of the support on the vessel such that the support can be inclined into the appropriate inclination for the undersea laying of the supply line, (C) means for controlling the pivoting of the support and for maintaining it at the requisite inclination, (D) means for depositing the new supply line part on the support, and (E) a workstation equipped with means for performing the assembly of the two supply line parts and ancillary tasks.
Examples of such apparatuses are described, in particular, in the following patents: U.S. Pat. No. 3,680,322; U.S. Pat. No. 5,421,675; U.S. Pat. No. 5,464,307 and U.S. Pat. No. 3,860,122.
In these embodiments, the workstation is carried by the support and means are required to ensure that this station retains the appropriate attitude, which is generally a substantially horizontal position at the assembly post, whatever the inclination of the support.
This is because the inclination of the support for laying may vary in accordance with the applications, since it depends on various factors including, in particular, the nature of the piping to be laid and the depth of laying.
An apparatus is also known which comprises a supply line support and a workstation which is carried not by the support but by the vessel, the support being fixed and the means for supporting the weight of the supply line part already submerged before assembly takes place being carried by the workstation (EP 0,478,742).
One of the objects of the invention is to allow the use of a workstation carried by the vessel and not by the support, in the case of a variable inclination support, which confers numerous advantages (simplicity, efficiency, etc.).
This is achieved, in accordance with the present invention, by arranging the pivot of the support so that it intersects the longitudinal axis of laying substantially in the said plane of assembly.
Under these conditions, the situation of the workstation for working is substantially independent of the inclination of the support, and the workstation can be carried by the vessel at a specific location.
In practice, nevertheless, it may be desirable to provide the workstation with a certain freedom of movement on the vessel in order to adapt it as well as possible to the inclination of the support.
The possibility of movement may also be desirable in order to change the nature of the work and, for example, to change from an assembly operation to a coating or monitoring operation.
Finally, the possibility of movement may be desirable in order to retract the station so as not to obstruct the tilting of the support if the support has to be folded down on the deck to make allowance for sea conditions or with a view to a major movement by the vessel.
Assembly by welding is preferred, but the invention is not confined to this form of assembly. In particular, as an alternative embodiment, provision is made for assembly to be undertaken by screwing, sliding fitting or an assembly connector.
Embodiments according to the present invention also possess one or more of the following features:
means having a curvature for guiding, on the support, a continuous supply line coming from a drum,
a beam and means for adjusting and maintaining the beam in position when it is in an inclined position, the beam furthermore being equipped with means having a curvature in order to guide a continuous supply line, coming from a drum, towards the support when the beam is in this position,
the means having a curvature possess a chute,
the means having a curvature possess a pulley,
the beam has a U-shaped upper end,
the means for maintaining the beam in position possess means for locking the beam to the support which comprise a structural link, associated with a bolt,
the support is a tower of metal girders shaped to allow a displacement of the workstation through or within the support,
the workstation is displaceable on rails rigidly fixed to the vessel,
the workstation is displaceable parallel to the longitudinal axis of the vessel,
the workstation possesses a floor for the movement of personnel and a ceiling and/or a ceiling-type structure which bears necessary means for supplying power to welding heads mounted to be displaceable substantially in the assembly plane,
the workstation possesses a ceiling and a floor which have channels for the passage of the end of the submerged supply line part and of the new supply line part,
the workstation possesses a rotating turntable equipped with means for supplying power to welding heads,
the rotating turntable is carried by a ceiling of the workstation or by a ceiling-type structure,
the turntable is capable of translational displacement within the station between an operating position and a retracted position,
the workstation comprises a turntable equipped with means for carrying out the said assembly and a turntable equipped with means for carrying out coating operations on the area of assembly, these two turntables being carried by fixed ceiling-type structures or on a ceiling of the station and being displaceable so as to be capable of substitution one for the other,
the workstation possesses control means rigidly fixed to an articulated arm which is itself rigidly fixed to a fixed support,
the workstation is a cabin whose position relative to the axis of the vessel can be adjusted as a function of the inclination of the tower,
the apparatus possesses two workstations respectively equipped with means for assembly and means for carrying out coating of the assembly, these two stations being movable in order to be able to be substituted one for the other in the operating position.
The invention applies, inter alia, to the laying of a supply line consisting of rectilinear sections or strings assembled and laid by stages, each section itself being capable of comprising a plurality of basic lengths of supply line assembled in order to form a string. These basic lengths are generally 12 meters.
It is advantageous, in order to deposit a new string on the support, to use a beam adapted to support the new string and to pivot about a substantially horizontal pivot axis of the beam, preferably the pivot axis of the beam coinciding with the pivot axis of the support, means being provided to control the tilting of the beam between a substantially horizontal starting position, which enables the string to be laid or formed on the beam from a stock, and an inclined transfer position where the string can be transferred to the support, which will previously have been brought into its inclined operating position.
This beam is, for example, articulated on the pivot of the support or is compelled to move in an arc of a circle centred on that pivot.
These two examples of embodiment will be described in due course.
The invention also applies to the laying of a supply line formed from rigid or non-rigid sections rolled up on a distributor and unrolled as required onto the support, with restoration of the section to a rectilinear configuration at the head of the support if necessary.
Another aspect of the invention relates to the use of tensioners adapted to grasp a supply line, upstream of the pivot, on a supply line support mounted pivotably on a vessel in order to be able to adopt any inclination required for the laying of the supply line.
Tensioners adapted to grasp a supply line and to apply to it a retaining force directed upwards along the axis of the supply line are commonly used by the person skilled in the art and are available on the market. Mention may be made, for example, of the tensioners made by Huisman Special Lifting Equipment b.v. and publications U.S. Pat. No. 5,823,712 and WO 98 50719.
According to the present invention, the tensioners are mounted displaceably on the support between two positions corresponding to a principal laying axis and a secondary laying axis, offset from but parallel to the principal axis.
It is thus possible to use the tensioners to hold and guide a supply line part or a supply line along either of the laying axes.
It is also possible, in conjunction with another apparatus, used to hold a supply line along a first laying axis, to hold and guide, by virtue of the tensioners, an auxiliary supply line, for example a cable, along a parallel laying axis.
These tensioners may therefore advantageously be used in conjunction with a laying apparatus according to the first subject of the invention.
According to another aspect, the invention relates to an apparatus for the connection and laying of the successive parts of an offshore supply line from a vessel, which comprises on board the vessel
a variable inclination supply line support equipped with means for supporting the weight of the already submerged supply line part and keeping available within an assembly plane the above-water end of this supply line part, means for receiving a new supply line part in accordance with the longitudinal axis of laying of the supply line and bringing it into the said assembly plane, and guide means,
means constituting a horizontal pivot of the support on the vessel such that the support can be inclined into the appropriate position for the undersea laying of the new supply line part,
means for controlling the pivoting of the support and for maintaining it at the requisite inclination,
means for depositing the new supply line part on the support,
a workstation equipped with means for performing the assembly, and
a beam adapted to support the new supply line part, this beam being mounted on the vessel in a manner such as to be able to pivot about the said pivot, and being provided with displacement means adapted to retain the new supply line part on the beam and to be displaced along the latter in order to bring the new supply line part into an assembly position in the assembly plane.
Advantageously, the displacement means are equipped with gripping means holding the new supply line portion during the manoeuvre of lifting the beam. These displacement means also make it possible to manoeuvre the new supply line portion accurately during its descent into an assembly position.
According to yet another aspect, the invention relates to an apparatus for the laying of an offshore supply line, unwound from a drum, from a vessel, which comprises on board the vessel
a variable inclination supply line support equipped with means for supporting the weight of the already submerged supply line part,
means constituting a horizontal pivot of the support on the vessel such that the support can be inclined into the appropriate position for the undersea laying of the supply line,
means for controlling the pivoting of the support and for maintaining it at the requisite inclination, and
a beam adapted to support a supply line, this beam being mounted on the vessel so as to be able to pivot about a substantially horizontal pivot axis of the beam preferably coinciding with the pivot of the support and comprising means for feeding and guiding a continuous supply line, these feeding means possessing a curvature such that the supply line can be guided on the supply line support without being damaged.
Advantageously, these feed means comprise a chute or a pulley.
Thus, it is made easier, at the shipboard crane, to install the feeding means on the beam rather than on the support. Similarly, it is made easier to install on the feeding means, at the shipboard crane and when laying begins, heavy items such as a heavy connector associated with a new supply line portion when the beam is located on the deck of the vessel.
Advantageously, the upper end of the beam, holding the chute or the pulley, is U-shaped to ensure the centring of the chute or the pulley. The effects of torsion on the beam are thus eliminated.
Advantageously, the beam is locked on the support by a structural link associated with a bolt. This makes it possible to release the tension of the cable intended to move the beam during the operations of laying the supply line.
The various aspects of the invention may be employed independently of one another or in combination.
Other aspects, features and advantages of the present invention will be more clearly apparent from a reading of the description which follows and which is given by way of illustration and not limitation, with reference to the attached drawings, in which the support is a tower.